1. Technical Field of the Invention
This invention relates to slide bar suspension systems used in snowmobile endless track suspensions; and more particularly to a slide bar with improved lubrication and cooling characteristics.
2. Background Art
On a tracked snowmobile, or sled as it may be called, an endless track contacts the snow or ground surface and by the use of a suspension system and motor driven sprockets, rotates the track beneath the sled to propel it forward. Slide bars or sliders or wear blades as they may be variously called, are a key component of the suspension system, having a relatively low friction sliding surface and bearing all or most of the weight of the sled upon the inside surface of the track. There are typically two parallel slide bars running lengthwise within the track; one on each side of the sled. The track rotates around the suspension system and slides under the bars as it contacts the ground surface. Prior art FIGS. 4 and 5 illustrate a typical track and suspension design. Track 1 revolves around suspension system 2, its path defined by the geometry of wheels 3 and slide bar 4. Holes 5 in track 1 admit loose material, be it snow, slush, water, mud, dirt, or what have you, that may be in the path of the snowmobile, into the area of the slide bar and suspension system.
Modern slide bars are typically plastic, in order to provide a low friction sliding surface and a low cost, relatively easily replaceable wear component. It is inherent in the design that the weight and speed of the sleds causes a tremendous heat build up between the track and the bars. The snow and water that penetrates openings in the track and is trapped between the track and slide bar, and impinges on the slide bars from the side, is under normal conditions adequately lubricious to hold down friction and keep the plastic rails within tolerable temperature limits so that friction, support and wear characteristics are not adversely affected.
However, heavier, faster sleds are being operated under ever more wide ranging and adverse conditions for both recreation and business purposes. It is not uncommon for sleds to be purposely run intermittently on surfaces where there is little or no snow or water to cool and lubricate the interface between the slide bar and the track, or on surfaces where debris such as dirt, sand, and gravel may contaminant the interface between the slide bar and the track. This abuse subjects the plastic slide bar to heat and mechanical stresses that increase friction and limit speeds, and quickly deteriorates or destroys the contact surface and/or the mechanical integrity of the slide bar.
A slide rail lubrication system with container, manual pump, and lines directing lubricant to the slide rails was disclosed in Reeve's U.S. Pat. No. 3,820,858. Devices for scavenging or scooping snow from along side the sled as it is in motion, and diverting it towards the slide bar for extra cooling, have been disclosed as in Rabehl's U.S. Pat. No. 4,036,320, further evidencing recognition of the cooling problem.
Lengthwise channels or grooves have been incorporated into the slide rail bearing surface of some slide rail designs, to channel snow and water trapped by the track through the groove for its cooling effect. This structural design leaves a continuous weak shoulder on the rail as is apparent from a cross section view, that is conducive to premature structural failure.
Diagonal channels or grooves in the rail contact surface, as disclosed in Russ, Sr.'s U.S. Pat. No. 3,887,242, have also been employed to enhance cooling, but this type of surface pattern breaks the continuity of the lateral edge support, and introduces a cyclic, longitudinal variation in the available support strength of the slider as the track passes longitudinally beneath the slider under the pressure of the vehicle and riders. The combination of the movement, pressure and the variation in support strength results in a low frequency bounce or vibration in the suspension system that is clearly noticeable to the rider. The ripple effect becomes more noticeable with wear, and at the same time causes wear to be uneven and accelerated, thus exacerbating the problem. The discontinuous lateral edge or shoulder structure weakens the slider and contributes to premature failure under the pressure and vibration. These disadvantages counteract any cooling benefit the feature might have provided.
In summary, excessive heat build up in the slider from the friction of the endless track during prolonged traverses over terrain that is other than snow or slush covered, has an attendant impact on performance and useful life of the slider, and remains a notable problem.